This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-338169, filed Nov. 2, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention particularly relates to an exposure method which is suitably performed under optimal focus conditions, an exposure apparatus, and a method of manufacturing a semiconductor apparatus in the manufacture of semiconductor elements, liquid crystal display apparatus, and the like.
2. Description of the Related Art
Recently, as an apparatus capable of reducing the diameter of a projection lens and the like, an exposure apparatus based on a scan exposure scheme (to be referred to as a scan exposure apparatus hereinafter) designed to perform exposure by moving a reticle and semiconductor wafer in opposite directions has been developed.
A focus control method in a scan exposure apparatus will be described with reference to FIG. 11. The uneven shape of the surface of a semiconductor wafer 104 to be exposed in an exposure area of the semiconductor wafer 104 is monitored in advance by a look-ahead focus sensor 112 (112a, 112b, and 112c). An arithmetic circuit mechanism 114 calculates a proper focus plane and tilt amount in the slit and scan directions from the monitoring result. Conventionally, scan exposure is performed while a semiconductor wafer stage 105 is tilted by a semiconductor wafer stage Z-axis driving mechanism 111 on the basis of the calculated focus plane and tilt amount. That is, the tilt of the semiconductor wafer with respect to the focus plane is corrected. Referring to FIG. 11, reference numeral 101 denotes a reticle; 102, a reticle stage; and 103, a projection lens.
FIGS. 12A to 12C and 3A to 3C show cases wherein the above focus control method is applied to semiconductor wafer surfaces. FIGS. 12a to 12C are views for explaining a case wherein a semiconductor wafer having no second- or higher-order component is exposed by using a conventional exposure method. FIGS. 3A to 3C are views for explaining a case wherein a semiconductor wafer having a second- or higher-order component is exposed by using the conventional exposure method.
With regard to the relationship between a semiconductor wafer surface (solid line) and the focus plane (dotted line) of the apparatus, if there is only a first-order component in the scan and slit directions (FIG. 12A), the semiconductor wafer plane is aligned with the focus plane by conventional correction (FIG. 12B). As a result, as shown in FIG. 12C, exposure is performed while the semiconductor surface remains unchanged with respect to the focus plane.
In practice, however, as shown in FIG. 3A, a second- or higher-order component, other than a first-order component, inevitably exists due to the influences of the flatness of a semiconductor wafer and aberration of the exposure apparatus. As shown in FIG. 3C, focus variations cannot be satisfactorily suppressed by only conventional correction in FIG. 3B.
This influence on a gently curved surface can be corrected in the scan direction in which the slit width is small, because correction is finely repeated in a scanning operation along the surface shape of the semiconductor wafer in the conventional method, as well. However, the influence on the curved portion in the slit direction cannot be corrected, and hence focus variations cannot be improved. This causes a deterioration in yield due to a focus error.
(1) According to an aspect of the present invention, there is provided an exposure method of performing scan exposure on an exposure area on a wafer by moving the wafer with respect to exposure light passing through an optical system in synchronism with movement of a reticle with respect to the exposure light, comprising:
measuring a position distribution, in an optical axis direction of the optical system, on a measurement area surface of the wafer which is not irradiated with the exposure light;
computing a tilt component and a curved component of the measurement area surface on the basis of the measured position distribution;
obtaining a leveling amount by which the measurement area surface is made to become orthogonal to the optical axis direction, on the basis of the tilt component;
obtaining an adjustment amount for an imaging characteristic of the optical system on the basis of the curved component; and
irradiating the measurement area with the exposure light on the basis of the obtained leveling amount and adjustment amount while the measurement area surface and the imaging characteristic are adjusted.
(2) According to another aspect of the present invention, there is provided an exposure method of performing scan exposure on an exposure area on a wafer by moving the wafer with respect to exposure light passing through an optical system in synchronism with movement of a reticle with respect to the exposure light, comprising:
measuring a position distribution, in an optical axis direction of the optical system, on a measurement area surface of the wafer which is not irradiated with the exposure light;
computing a tilt component and curved component of the wafer surface on the basis of the position distribution on the wafer surface;
measuring a position distribution, in the optical axis direction, on a reticle surface of the reticle which is located on the optical system side;
computing a tilt component and a curved component of the reticle surface on the basis of the position distribution on the reticle surface;
obtaining a leveling amount by which the measurement area surface is made to become orthogonal to the optical axis, on the basis of the tilt component of the measurement area surface;
obtaining at least one of adjustment amounts for imaging characteristic of the optical system and the position of the reticle surface on the basis of curved components of the measurement area surface and the reticle surface; and
irradiating the measurement area surface with the exposure light on the basis of the leveling amount and the adjustment amount while the measurement area surface and at least one of the imaging characteristic and the position of the reticle surface are adjusted.
(3) According to still another aspect of the present invention, there is provided an exposure apparatus comprising:
an optical system which projects a pattern image formed on a reticle onto a wafer;
a reticle stage on which the reticle is placed and which can move in a direction perpendicular to an optical axis direction of the optical system;
a wafer stage on which the wafer is placed and which can move in the optical axis direction of the optical system and a direction perpendicular to the optical axis direction;
wafer surface position measurement means configured to measure a position of the wafer surface in the optical axis direction of the optical system;
a computing mechanism which computes a tilt component and curved component of the wafer surface on the basis of the measurement value obtained by the wafer surface position measurement means;
adjustment means configured to adjust a position of the wafer in the optical axis direction of the optical system on the basis of the tilt component; and
correction means configured to correct an imaging characteristic of the optical system on the basis of the curved component.
(4) According to still another aspect of the present invention, there is provided an exposure apparatus comprising:
an optical system which projects a pattern image formed on a reticle onto a wafer;
a reticle stage which can move in an optical axis direction of the optical system and a direction perpendicular to the optical axis direction;
a vertical movement mechanism which is mounted on the reticle stage and changes a position distribution on the reticle in the optical axis direction of the optical system;
a wafer stage on which the wafer is placed and which can move in the optical axis direction of the optical system and a direction perpendicular to the optical axis direction of the optical system;
wafer surface position measurement means configured to measure a position of a measurement area surface of the wafer in the optical axis direction of the optical system;
reticle surface position measurement means configured to measure a position of the reticle surface located on the optical system side in the optical axis direction;
a first computing mechanism which computes a tilt component and a curved component of the measurement area surface on the basis of the measurement result obtained by the wafer surface position measurement means;
a second computing mechanism which computes a curved component of the reticle surface on the basis of the measurement result obtained by the reticle surface position measurement means;
adjustment means configured to adjust a position of the wafer in the optical axis direction of the optical system on the basis of the tilt component computed by the first computing mechanism; and
correction means configured to correct at least one of an imaging characteristic of the optical system and a position distribution on the reticle surface in the optical axis direction on the basis of the curved component computed by the first and second computing mechanisms.